A one-time password is a disposable password that is valid only once.
One-time password authentication by email is a method of confirming your identity by entering the one-time password that will be sent to the email address registered with your Expo ID.

https://www.expo2025.or.jp/wp/wp-content/themes/expo2025orjp_2022/assets/pdf/tickets-index/id_registration_manual_en.pdf